The isothermal sections of the Fe-Si-Cr-Al quaternary system at 800 °C with the Fe composition being fixed at 67 at.% and 50 at.% were determined experimentally using optical microscopy, scanning electron microscopy coupled with energy dispersive x-ray spectroscopy, and x-ray diffractometry. Two three-phase regions (BCC-A2 + σ + D0₃, FeSi + Fe₅Si₃ + D0₃) were found in the isothermal sections at 67 at.% Fe. Phase microstructures of Fe-corner in the quaternary Fe-Si-Cr-Al system were investigated, especially the multiphase regions containing bcc disordered phase and bcc ordered phases. D0₃ occupies almost half of the isothermal section and could maintain equilibrium with all phases (BCC-A2, σ, Fe₅Si₃, FeSi) in the isothermal section. One four-phase region (BCC-A2 + σ + Cr₃Si + D0₃) and five three-phase regions (Cr₃Si + D0₃ + BCC-A2, Cr₃Si + σ + BCC-A2, Cr₃Si + D0₃ + σ, Cr₃Si + Fe₅Si₃ + D0₃, FeSi + Fe₅Si₃ + D0₃) were found in the isothermal section at 50 at.% Fe.

Fe-Si-Cr-Al四元体系在800°C时的等温截面是用光学显微镜，扫描电子显微镜和能量色散x-射线光谱法通过实验确定的，其中Fe的组成固定为67at。％和50at。％。射线光谱法和X射线衍射仪。在等温截面中发现了两个三相区域（BCC-A2 +σ+ D0 ₃，FeSi + Fe ₅ Si ₃ + D0 ₃），Fe含量为67 at。％。研究了四元Fe-Si-Cr-Al体系中Fe角的相微结构，特别是包含bcc无序相和bcc有序相的多相区域。D0 ₃几乎占据了等温截面的一半，并且可以与所有相保持平衡（BCC-A2，σ，Fe ₅Si ₃，FeSi）在等温区中。一个四相区域（BCC-A2 +σ+ Cr ₃ Si + D0 ₃）和五个三相区域（Cr ₃ Si + D0 ₃ + BCC-A2，Cr ₃ Si +σ+ BCC-A2，Cr ₃ Si在等温截面中，铁含量为50 at。％时，发现+ D0 ₃ +σ，Cr ₃ Si + Fe ₅ Si ₃ + D0 ₃，FeSi + Fe ₅ Si ₃ + D0 ₃）。